The warning comes from an FDA analysis of suicidality -- suicidal behavior or thoughts -- in placebo-controlled studies of 11 drugs known collectively as "antiepileptics." The drugs are used to control seizures and to help control the symptoms of some psychiatric disorders.

"All patients who are currently taking or starting on any antiepileptic drug should be closely monitored for notable changes in behavior that could indicate the emergence or worsening of suicidal thoughts or behavior or depression," the FDA warned in a letter to health professionals.

In the clinical trials, patients receiving inactive placebo pills had a 0.22% incidence of suicidality. Those receiving the epilepsy drugs had a 0.43% incidence of suicidality -- twice that of placebo recipients, but still a very small risk.

The drugs were relatively more likely to be linked to suicidality when used to treat epilepsy than when used to treat psychiatric disorders or other conditions.